In small bowl, whisk together balsamic vinegar, maple syrup, mustard, garlic, thyme, cayenne and salt and pepper. Pour sauce into a large plastic baggy and add chicken breasts. (Tip: you can pound out the chicken breasts to ensure they each have the same thickness so they cook evenly). Marinate the chicken for at least 30 minutes or even overnight.
Heat olive oil in a large skillet over medium-high heat until oil shimmers, about 3 to 4 minutes. Using tongs, remove chicken breasts from baggy (leaving the marinade inside) and arrange in the pan. Allow chicken to cook for about 7 to 8 minutes, without moving, so a nice golden-brown crust forms. Flip chicken over and cook the other side for another 7 to 8 minutes. You'll know the chicken is done when the juices run clear and the inside temp has reached 160 to 165°F.
Remove chicken and place on a cutting board to rest then pour the remaining marinade into the heated skillet. Scrape up any brown bits and allow marinade to bubble up and cook, stirring occasionally.
Add chicken back into the skillet, coating well. Serve and enjoy!